2009 Ford F250 super duty v8

I have towed 16,700 miles at 15,600 lbs combined with a similar truck. Spent 2 months in the Rockies and crossed a half dozen 10K plus passes. The only time my truck struggled was on a 1 mile stretch of road from downtown Central City, CO going to the KOA at the top of the hill. Starts at 11% grade up to 17% then down to 10% near the end. I made it but never got out of 1st gear. 4200 RPM is my sweet spot in the mountains whether at 65 in 3rd gear or 45 in 2nd gear. Engine braking is fantastic and the temps stay consistent. The highest tranny temp I have seen (Scangauge) is 202 and high water was 211 coming down Loveland Pass at 4400 RPM in 2nd gear. Rarely have to use the brakes coming downhill, in fact I now have 75K miles on the truck and am still on the original brakes shoes. If you can find a V10 buy it, if not the V8 will do the job.